Method for processing surface detected seismic data to plotted representations of subsurface directional seismic data

ABSTRACT

Individual geophones of a surface array of geophones detect the arrival of energy transmitted into the earth from a seismic source and reflected from subsurface reflectors. A record of traces of seismic data is a time based recording of signals representing the reflection energy (called events) detected by each individual geophone. When the geophones are treated as an array, the energy detected by the array may be analyzed to provide both amplitude and direction identification for the reflected energy. By systematically processing the record of traces representing the energy reflected to the geophone array it is possible to isolate directional energy, to pick reflection events within the isolated energy and to plot these selected events along a directionally distinct representation of the subsurface path of seismic energy from the surface source to the subsurface reflector and back to the surface geophone array.

Unite States Patent [1 1 Stephenson Oct. 16, 1973 METHOD FOR PROCESSING SURFACE DETECTED SEISMIC DATA TO PLOTTED REPRESENTATIONS OF SUBSURFACE DIRECTIONAL SEISMIC DATA [75] Inventor: Lee P. Stephenson, Fullerton, Calif.

[73] Assignee: California Research Corporation,

San Francisco, Calif.

[22] Filed: June 8, 1970 [21] Appl. No.: 44,648

Related US. Application Data [63] Continuation of Ser. No. 416,947, Sept. 24, 1964,

abandoned.

[52] US. C|.340/l5.5 DS, 340/15.5 R, 340/l5.5 CP,

346/33 C [51] Int. Cl. GOlv 1/24, GOlv l/28 [58] Field of Search 340/155 DS, 15.5 CF; 346/33 C [56] 7 References Cited UNITED STATES PATENTS 2,144,812 l/l939 Rieber 340/15.5 2,914,854 12/1959 Westphal 340/15.5 X 3,038,661 6/1962 Klein 340/155 X 3,127,585 3/1964 Alexander et a1. 340/l5.5 3,149,302 9/1964 Klein et a1. 340/155 3,149,303 9/1964 Klein et a1. 340/155 Primary ExaminerBenjamin A. Borchelt Assistant Examiner-H. A. Birmiel Attorney-A. L. Snow, F. E. Johnston, C. J. Tonkin and G. W. Wasson [57] ABSTRACT Individual geophones of a surface array of geophones detect the arrival of energy transmitted into the earth from a seismic source and reflected from subsurface reflectors. A record of traces of seismic data is a time based recording of signals representing the reflection energy (called events) detected by each individual geophone.

9 Claims, 23 Drawing Figures PATENTEDUEI 16 ms SFEH 010? 14 ASTER RECORDER n! PAIENIEDncns ms 3.766519 sum UEHF 14 MAJOR LOBE 1 OF ARRAY I I I I I I O5 I I A A A A A INCOMING SIGNAL DIRECTION E 2 F r- 3 F|G.6 FlG.7

a b c d INVENTOR LEE R STEPHENSON BY a FIG.5 Ql6wu4m- TTORNEYS PAIENTEBUU 15 ms 3. 766.519

sum 030E 14 LOCATIONAL TRACES ONE TRACE FOR EACH GEOPHONE RECORDED GEOPHONE SIGNALS FIELD RECORDING DEVICE I 'I'I'I'I'I'I'I'I'I'I'I'I' GEOPHONE SIGNALS PUNCHED CARD I READER I I STATIC CORRECTIONS III| | I I |Il I I IIIl HHI D/A I A omzcnon CONTROL DYNAMIC CORRECTIONS CONVERTERS A 4- L 1: MULTI-TRACE UNPEICTIEO 0+ SUMMATION 23:?

I AMPLIFIER I INTER- POLATING POTENTI- OMETERS 20 MATI 'J SUPPLY MULTI-TRACE a AUTO c 3 PICKING 1 27 55 RECORDER CIRCUIT D I 25 l x-Axls Z-AXIS 28 V v I I 3; 4/0! 30 10 I05 I 29 PATENTEU BT 3,766,519 SHEET 05 HF 14 I O "'2 a IN AMP. Jfi DIFFERENTIATOR AMPLIFIER AND CLIPPER T-FL T T1 T T T1T2T3 FULL wAvE RECTIFIER W DIFFERENTIATOR TOT T2 T3 5 l T1 T2 T3 65 T2 T3 GATE SCHMITT SYNCHRONOUS TRIGGER DEMODULATOR 70 J T0T1 2 T3 67 66 1I =5 IE 1 f SCHMITT Q|NIDENE SCHMITT H m G H TRIGGER CH.1 DETECTOR TRIGGER CH.5 uJ Lu 2 z 2% z o o u- I m I U U 7 COMPARATOR COMPARATOR CH.3 & cI-I.I CH.3 & cI-I.5 7/ 74 COMPARATOR coMPARAToR -vR MAx. vR MIN. (MAXIMUM) (MINIMUM) COINCIDENCE DETECTOR l PI oTTING PLOTTING CR TUBE INTENSITY CONTROL INVELN'TOR DELAY CHANNEL 3 LINE AME LEE P. STEPHENSON SIGNAL At BY j mi failo FIG. 11 w PATENTED UB1 16 I973 SEEN 07 0F 14 INVENTOR PATENTEDUBI 1 6 I973 SNEH 080$ M INVENTOR LEE P. STEPHENSON lgu/r QZMZL TQRNLYS FATENIEDUCHS 97s 3.766519 am: as Q? 14 REFLECTION TIME (SEC) REFERENCE INVENTOR LEE P. STEPHENSON MToRNEYs mammal 1 m 3.766519 sum was 14 INVENTOR LEE R STEPHENSON ATTORNEYS PATENTEDBCH61973 3766519 SEE 12 0F 14 PATENTEDUU 18 E173 SHEET 1'30! 14 INVENTOR LEE P. STEPHENSON TORNES PATENTEDBBT 16 an 3766; 5 1 9 SIEET 1M? 14 INVENTOR V LEE P. STEPHENSON TTORNEYS METHOD FOR PROCESSING SURFACE DETECTED SEISMIC DATA TO PLOTTED REPRESENTATIONS OF SUBSURFACE DIRECTIONAL SEISMIC DATA This application is a continuation of Ser. No. 416,947, filed Sept. 25, 1964, now abandoned.

This invention relates to a method and apparatus for automatically processing and displaying seismic data. In accordance with this invention, information in the seismic data relating to underground earth formation may be automatically processed to a resulting display representing the underground formations in their proper spatial positions with respect to a reference point at or near the earths surface. Furthermore, the processing and resulting display of the data is done without the necessity for intervening human examinations, measurements, or calculations. This application is a continuation-in-part of my copending application Ser. No. 803,906 filed Apr. 3, 1959 for Automatic Seismic Data Processing Method and Apparatus, now abandoned in favor of this continuing application.

Present day methods of seismic surveying involve the initiation of a seismic wave in a geological mass through which the seismic energy is transmitted to be reflected and refracted by the discontinuities in acoustic impedance associated with interfaces between the rock layers, or strata within the earth. Reflected, refracted and diffracted energy from these horizons within the earth is detected at a plurality of geophones distributed over the earth s surface, and a record, preferably in some reproducible form, is produced of the series of individual signals from each of the surface geophones. This record indicates, as a function of time, the mechanical movement of the earth at the location of each of the geophones due to energy received from reflecting or refracting horizons within the earth.

Prior art systems for analysing information contained in seismic records have disclosed methods for making the static and dynamic time adjustments between the signal traces from the various geophones necessary to produce a corrected printed record indicating the energy received at the earths surface by the several geophones. From this record an experienced seismologist may draw certain inferences regarding the subsurface structure within the geological mass being surveyed. From measurements indicating the elapsed time between the initiation of the seismic wave and the arrival of the returned energy at each of the several geophones, the attitudes and the distances of the reflecting or refracting horizons from the point of generation of the seismic waves may be determined if, in addition, certain velocity information is known or assumed about the earth materials.

In the normal course of analyzing such a record, the seismologist must first pick the record; that is, he must detect by visual observation of the recorded information all evidence for the presence of coherent reflected or refracted energy, and note the times of arrival of such events at each of the several geophone locations. From these arrival times and a knowledge or estimation of the seismic velocities, he can then compute, by any of several well-known methods, and plot to a suitable scale, the positions in the earth of the geological features responsible for the appearance of the events upon the seismic record. The seismologist may also make use of the distinctive appearance or character, of the seismic events in following them from record to record and in associating them with particular geologic features. The resulting synthesized picture of the subsurface geometry derived from the picked and plotted events is commonly referred to as a migrated seismic section, and the individual seismic events whose positions have been computed and plotted relative to a reference point are said to have been migrated.

It is commonly found that the visual detection of coherent energy is rendered difficult by the presence of interfering noise upon the seismic record. This noise may be caused by external factors such as wind, traffic, and the movements of large animals; but of even greater importance is the noise associated with the initiation of the seismic wave and appearing in such forms as ground roll, hole noise, and energy scattered from minor geological discontinuities. In addition, the reflected or refracted events of interest often interfere with each other, especially in those cases where the subsurface geometry is relatively complex. The sum total of noise and interference tends to obscure the reflected or refracted events of interest, making their detection more difficult and resulting in inaccuracies in the determination of their arrival times and characters. Thus, the independent analysis of a seismic record by each of several seismologists may produce different interpretations based upon the same seismic information, for an anylsis is, to a certain extent, an arbitrary determination governed by the experience and ability of the seismologist making it.

This serious drawback to the interpretation of seismic information was early recognized by Frank Rieber in several of his published articles. His early work has resulted in the issuance of many patents in his name, including U.S. Pat. No. 2,144,812, issued Jan. 24, 1939, entitled Method of Geophysical Exploration," wherein a method has been described for deriving information infomation from energy received at a multistationed surface geophone spread. In this present specification, reference will be made to certain conceptions of Rieber; however, in the most part these references will be to information derived from early suggestions made by Rieber that have been expanded and improved. These references to Rieber are made, in the light of present day advances in seismology, and must be considered in that light in order to appreciate their true relevance to the material of the present specification.

The method of the noted earlier patent to Rieber involved the repeated combining or summing of the recorded signals from a plurality of surface geophones. Each sum was made with the original signals relatively delayed with respect to each other. In the Rieber method the relative delay imposed between signal traces from neighboring geophone was the same from geophone to geophone in any individual combination or sum. However, each individual combination or sum employed a different repetitive time delay between the signal traces, consistent throughout that individual combination or sum. The purpose was to use the fact that when seismic energy is returned to a surface geophone spread, the wave front of the energy will encounter the individual geophones in a determinable order established by the direction from which the energy is returning. In the system suggested by Rieber, a new multitrace record of combined geophone signals was produced by the method of scanning across the original multitrace record at incrementally different angles to the time axis of the original record. A separate trace was produced on the derived record for each of the incrementally different transverse scans of the original record so that each of the separately recorded traces would contain information for incrementally different relative time delays between the geophones. Through these incrementally different transverse scans of the original record, all signals of the original seismic record were summed in new combinations, and where a returned wave had energized successive individual geophones in a particular sequential order, the scanning of the original seismic record in accordance with this sequential order of reception would produce an enhanced signal. The enhanced signal was produced when the transverse scanning established, in effect, a synthesized array of geophones parallel to the wave front of the reflected energy as it returned to the earths surface. Any signals arriving at the geophone array in a time-sequential order other than that produced by energy returning to the array from a direction corresponding to the particular angle of transverse scanning of the original record would tend either to cancel or to obscure each other, whereas signals arriving at the geophone array in the correct time sequence would be additive, and in effect, series enhanced.

This present application is related to a method employing some of the Rieber suggestions and is directed to a system for further analyzing the information contained in a conventional seismic record and for the use of this information to actuate a seismic data display apparatus whereby information concerning subsurface reflecting or refracting horizons within the subsurface earth strata may be plotted automatically to eliminate the necessity for prior interpretation by an experienced seismologist. In accordance with the method of the present invention, the seismic traces derived from seismic signals received by a multigeophone spread at the earths surface are first adjusted for the static and dynamic time corrections well known to, and commonly applied by, those skilled in the art of seismic surveying. From this corrected seismic record, a multitrace beam-steered" record is produced through repeated seismic trace combinations, and from beam-steered record and appropriate velocity data, an automatic plotting device is actuated to provide a migrated display of the information received at the geophone array. The method may further be modified to include automatic event picking through application of signal strength and signal direction-of-arrival criteria so that the plotting of the information contained in the original record may be automatically restricted to the significant seismic reflections within the record.

The object of the present invention, therefore, is an automatic seismic data processing and display apparatus and the method and apparatus for analyzing seismic data whereby information derived from a geophone spread at the earths surface may be automatically analyzed and processed for eventual automatic plotting on a display surface in a manner such that reflecting or refracting horizons within the earth may be represented in their proper positions in space.

A further object of the present invention is a novel method of display of seismic information whereby common human errors are eliminated, the true character of the seismic signal is preserved, and the complete analysis of seismic data is made with greater accuracy and rapidity.

A further object of the present invention is a novel display of seismic data in the form of directional graphical seismic traces.

Further objects and features of the invention will be fully apparent to those skilled in the art from the specification and appended drawings illustrating certain preferred embodiments in which:

FIG. 1 is a sectional view through a geological mass illustrating representative paths for seismic energy;

FIG. 2 is a sensitivity graph for a geophone array of particular geophone spacing;

FIG. 3 is a graphic representation of the change in directional selectivity of an array of geophones as the major lobe of an array is moved with respect to a seismic signal source;

FIG. 4 is a block diagram of an apparatus for automatically plotting seismic information in the method of the present invention;

FIG. 5 is a graphic illustration of reflected energy being received at a geophone array;

FIGS. 6 and 7 are portions of multitrace records of energy received in the directions as illustrated in FIG.

FIG. 8 is a composite of the portions of multitrace records of FIGS. 6 and 7;

FIG. 9 is a portion of a beam-steered record as prepared as indicated in FIG. 8;

FIG. 10 is a block diagram of an apparatus for automatically picking seismic data;

FIG. 11 is an alternative form of an apparatus for automatically picking seismic data;

FIG. 12 is a series of wave form diagrams related to the automatic picking apparatus of FIG. 11;

FIG. 13 is an actual seismic record to greatly reduced scale of locational seismic traces from a geophone spread of twenty-four geophones;

FIG. 14 is a record of directional seismic traces produced from the locational traces of FIG. 13;

FIG. 15 is the record of FIG. 14 with events automatically picked;

FIG. 16 is a migrated straight ray display of directional seismic traces;

FIG. 17 is a migrated straight ray display of directional seismic traces with significant seismic events automatically picked and accentuated in predominance within the display;

FIG.. 18 is a migrated curved ray seismic display of the directional seismic traces of FIG. 14;

FIG. 19 is a migrated curved ray display of the automatically picked directional seismic traces of FIG. 15;

FIG. 20 is the display of FIG. 19 with a conception of a geological formation in cross-section superimposed upon the display to illustrate reflecting horizons that could produce the record of FIGS. 13-19;

FIG. 21 is a display of a plurality of migrated curved ray seismic records spaced with respect to each other in accordance with the positioning of the geophone spreads at the earth's surface;

FIG. 22 is a portion of a sonograph record;

FIG. 23 is the record of FIG. 22 showing the application of full event picking criteria.

In the art of reflection seismic surveying, a seismic impulse is initiated at or near the earths surface to establish an elastic wave for transmission through the earth. Any discontinuity or variation in the structure within the earth will reflect, refract, or diffract this wave train, or a portion thereof, so that the record made at a receiving point will comprise a number of arriving waves, each derived from the original impulse, and each differing from the others in time of arrival or in magnitude or both. Generally speaking, seismic energy will be reflected by subsurface formations that are substantially tangent to the wave front as it travels through the earth formations. The energy reflected by the subsurface reflectors will return to the earths surface-in the form of elastic movements of the earth formations. These movements then may be detected by individual geophones and converted to electrical signals for the production of reproducible traces on a reproducible recording means. These traces willhereinafter be referred to as locational seismic traces. The information in each of these seismic traces contains, among other things, the elapsed times between the initiation of the seismic impulse and the arrivals of the various individual events along the seismic trace.

Referring now to FIG. 1 wherein a faulted subsurface formation of a geological mass is illustrated, it may be seen that at least some of the information derived from the seismic motion detected by the geophone spread at the ea'rths surface will be contained in reflection events from reflector 9 and reflector 10. For the purpose of this illustration, only five geophones 11 are illustrated as positioned at the surface of an earth formation 12 wherein the reflectors 9 and are located. The geophone spread is positioned about a hot point 13, here shown at the center of the spread, and may consist of many more geophones than the five illustrated.

As energy is transmitted from the shot point 13 into the earth'formation 12, it strikes discontinuities at the reflecting horizons 9 and 10 causing reflections to be returned to the geophone spread along paths such as 14, 15, 16 and 17. Because the reflector 9 is directly below the shot point 13, the energy will be reflected substantially vertically to the geophone spread. Under the conditions intended to be represented in FIG. 1, reflector 9 is of such distance below the earths surface that the wave front of the reflected energy is substantially parallel to the earths surface when it arrives at the geophones 11 within the spread. The seismic energy travelling along paths l4 and will arrive at each geophone within the spread at substantially the same elapsed time so that the record produced by the geophone spread will contain an event at substantially the same elapsed time along each trace. However, the energy from the tilted reflector 10 that returns along paths l6 and 17 will be received at different elapsed times by the geophones within the spread. The separate traces produced by the separate geophones for the reflection from reflector 10 will show the event arriving at different elapsed times. Part of the energy received by the individual geophones 11 at a particular instant and reproduced on its seismic trace could be reflected from both reflectors 9 and 10 since some parts of these two reflectors are approximately the same distance from the shot point 13. Because of this coincidence in time, the combined energies of the two reflections could intermingle and be substantially hidden one in the other so that neither reflector would be easily defined by simple inspection of the conventional seismic record.

In accordance with certain of the early concepts of Rieber, it is possible to combine the signals received by the several geophones to select directional seismic information. To accomplish this selection in the manner of the present invention, the geophone spread becomes in effect a directionally sensitive geophone array. The array will have directional sensitivity in a lobe or beam pattern similar to that shown in FIG. 2 and the directional sensitivity lobe or beam may be moved in discrete steps by selectively adding incrementally timedelayed signals from the traces produced by the individual geophones. Each of the selectively added combinations of the relatively delayed signals may then be considered as a separate record'trace of directionally received seismic energy.

FIG. 2 indicates the directive characteristics of a geophone array, showing the relative strength of the signal that would be recorded by the array of geophones if the time delay combination of the geophone outputs were to be held constant and the direction of an incoming constant amplitude signal were to be moved in the plane passing through a linear array of geophones, angularly about the center of the array. It can be shown mathematically that for transient signals of the character generally encountered in seismic work, the width of the directivity pattern or, as it is sometimes called, the sensitivity lobe, is related to the dominant period of the seismic signal. When compared to the response which results when the signal arrives simultaneously at all geophones in the array, the amplitude of the response will be reduced by approximately one-half when the signal arrives at one end of the array 0.6 of a period before it arrives at the other end.

Just as the response varies if the direction of the incoming signal changes while the relative time delay interval of the geophones is held constant, so does the response vary when the relative time delay of the geophones is changed while the direction of the incoming signal remains constant. In FIG. 3 the incoming signal is indicated to be coming from a fixed direction, namely from vertically below the geophones. The five different parts of the FIG. 3 are intended to represent the same set of geophones time delayed in five different ways so that the directional sensitivity is a maximum in five different directions. In practical geophysical prospecting, it is necessary to decide in how many different ways to time delay the signals-received by the geophones, or in effect, in how many different directions to point the sensitivity lobe of the geophone array. Each direction corresponds to a different set of relative time delays between the received geophone signals, and the combining of each set of locational traces into a set of directional traces requires a significant amount of time and effort, no matter by what specific method it is done. Therefore, it is of interest to know the fewest number of directions that the sensitivity lobe may be pointed without missing a significant signal coming from some direction intermediate to two of the chosen directions. Both theory and experiment have been used in deciding what is the best number of directions. It has been found best in the usual case to vary the direction in steps such as indicated in FIG. 3. In each directional step, the time delays between the geophones are changed so that the imposed total delay, between the end geophone traces will change by approximately 0.3 of the dominant period of the seismic energy being received. It will then require two directional steps for a new sensitivity lobe to be pointing in the half-amplitude direction of a previous lobe.

When the seismic signal is of very poor quality, it has been found advantageous to sample oftener, changing direction by steps such that the total imposed time delay between the geophone traces changes by only 0.1 of the dominant period of the energy being received. On the other hand, when the signals being received are of very good quality, with little noise, it is sometimes adequate to change direction in large steps such that the total imposed time delay between end geophone traces changes by 0.6 of the dominant period of the energy being received. A suitable range of change in the total imposed time delays between end traces is, therefore, 0.1 to 0.6 of the dominant period of the seismic energy being received, with the intermediate value of 0.3 being the usual optimum.

It has now been shown how a multigeophone seismic record contains information that may be directionally selected and how the signals from individual geophones within a spread should be relatively delayed to provide for optimum reception characteristics when combined. It should be understood that the manipulation of time delays between geophones within the spread is not accomplished by actual physical movement of the geophones nor is it usually accomplished by time delaying individual signals in an initial recording. The directional manipulation of the geophones as an array is usually accomplished after the original geophone signals have been recorded in a conventional reproducible seismic recording in which the signals received by the individual geophones are separately recorded; however, the relative time delays could be imposed on the signals prior to the initial recording.

In the usual beam steering process, in which the seismic signals are first directly recorded on a reproducible recording medium, the original traces are transformed during subsequent reproduction using movable reproducing heads or similar devices and suitable summing circuits. A second record is produced of the combined or summed signals from the geophones with the original individual geophone signals relatively delayed or advanced in time, in accordance with a predetermined directional sequence for the steering of the geophone array. Each of the different summations or original geophone outputs will produce a separate trace and each of these separate traces will be recorded as directional information detected by the array hereinafter referred to as a directional seismic trace.

Reference should now be had to FIGS. through 9 where the production of a beam-steered record is indicated in graphic form. FIG. 5 illustrates a geophone spread including a plurality of individual geophones 11 with the central four of the spread identified by letters a, b, c, and d. Possible paths of reflected seismic energy through an earth formation are designated by the arrows 1, 2, and 3, indicating energy arriving from directly below the spread and to each side of below the spread. Arrow 1 indicates a typical direction from which no reflection energy is returning. FIG. 6 illustrates signal traces on a multitrace seismic record for the reception of energy arriving in the direction of the arrow 2. In these signal traces, it may be seen that each of the geophones detects seismic energy at the same time. FIG. 7 illustrates the reception of energy in the direction of arrow 3 wherein the trace a3 receives the energy first and each of the subsequent traces i b c (1;, receive their energy at some time differential after the first reception of energy at the geophone 0 The traces of FIGS. 6 and 7 would indicate the reception ofenergy if the energy coming from the directions 2 or 3, respectively, were the only energy to be received at the geophone spread. FIG. 8 illustrates the composite grouping of the two signals of FIGS. 6 and 7 as they might appear if they arrived together at the geophone spread, as for instance, if reflected from horizons 9 and 10 of FIG. 1. Each of the wiggles of the traces a, b, c, and d of FIG. 8 would be a combination of the information found in the traces of FIGS. 6 and 7 wherein trace a would comprise the algebraic sum of the signals as illustrated in FIGS. 6 and 7, trace d would illustrate the signals arriving at two different times such that neither signal would amplify or destroy portions of the other signal, and traces b and c would indicate intermixing of the two signals.

Also shown in FIG. 8, in the form of dotted lines designated l, 2 and 3, are three different relative time delay relationships for combining the signals found on the composite record. The relationships, as shown, would be those for selecting the signals arriving in the directions corresponding to the arrows shown in FIG. 5. Summing the signals along the line designated 1 would produce a signal as is illustrated in FIG. 9 on the trace designated 1. It should be understood that this signal would show no coherent energy coming from the direction of arrow 1 to the right side of the spread as shown in FIG. 5. The trace designated 2 would be the sum of the signals of the FIG. 8 record in the time delay combination shown in the dotted line 2, and the trace designated 3 would be the combination in the timephase direction of the dotted line 3 of FIG. 8. In that no coherent energy is received from the direction designated by the arrow 1, the time delay combination represented by trace 1 of FIG. 9 illustrates no substantial energy. However, traces 2 and 3 of FIG. 9 illustrate coherent energy from the directions which correspond to their respective time-lagged combinations of the geophone signals or, stated differently, they display the directionally included information contained in the original seismic record from the geophones now connected as an array. It should be understood that there would be several separate traces separating traces l, 2 and 3, with each trace being a different summation combination of the multitrace record of locational seismic traces. The strong signal shown on trace 3 would therefore appear on adjacent traces at lesser amplitudes as the sensitivity lobe of the geophone array was swept past the true direction of the reflector causing the energy arriving in the direction of arrow 3.

When an entire record as illustrated in FIG. 13 has been processed in the manner of FIGS. 5-9 with the beam or sensitivity lobe of the geophone array moved in the selected number of steps in accordance with the foregoing analysis, a plurality of individual directional seismic traces will have been produced with a separate trace for each of the selected steps of directionality for the geophone array. These separate traces may be collected into a full record and may be displayed as parallel traces in the manner illustrated in FIG. 14 and hereinafter called a sonograph record" following the nomenclature established by Rieber. The sonograph record itself may be useful over and above the conventional seismic record. Perhaps the best present use to which an unmodified sonograph record may be put is that of aiding a seismologist in the picking of a conventional record. It is sometimes possible to see certain 

1. A method for the complete automatic plotting of directional seismic traces formed by summing geophone signals time-delayed with respect to each other, taking into account seismic velocity variations within the earth, so that the plotted mean positions of said directional traces represent actual approximate wave ray paths in the subsurface, said ray paths being both curved and distorted in scale so that the variations in amplitude along said traces represent the geologic features which gave rise to said variations in amplitude, said features being represented in approximate true subsurface depth and offset, comprising the steps of: a. machine generating amplitude values for a directional seismic trace by summing a plurality of side-by-side amplitude-versustime locational seismic traces, said locational traces being relatively time-delayed with respect to each other, b. repeating step (a) to generate amplitude values for a plurality of directional seismic traces wherein each trace corresponds to a distinct and different moveout corresponding to the difference in arrival time of the seismic waves which caused said locational traces; and c. recording at least portions of said directional seismic traces upon a display surface in a form wherein each of said directional seismic traces appears to emanate from a point representing a mean location on a datum surface within the earth under investigation, and each of said directional traces proceeds away from said point into the earth under investigation in accordance with the detected directional siesmic information it represents and in accordance with the velocity ditribution of said seismic waves within said earth under investigation.
 2. The method of claim 1 wherein subsurface velocity data are used to modify the directions and the scales of plotting of said directional traces as they proceed along said display surface.
 3. The method of claim 1 wherein the amplitudes of selected segments of at least some of said directional seismic traces are modified to emphasize the occurrence of seismic events, said sgements being selected by predetermined coincidence criteria applied in trace-to-trace comparisons of adjacent directional seismic traces.
 4. The method of claim 1 wherein successive neighboring directional traces are produced by changing the total relative time delay imposed across said plurality of locational traces by an amount between 0.1 and 0.6 of the dominant period of the received seismic waves.
 5. The method of claim 1 wherein successive neighboring directional traces are produced by changing the total relative time delay imposed across said plurality of locational traces by 0.3 of the dominant period of the received seismic waves.
 6. The method of claim 1 in which steps (a), (b) and (c) are repeated for a plurality of sets of locational seismic traces from a corresponding plurality of geophone arrays appearing to emanate from a plurality of locations on said datum surface along a line of seismic survey.
 7. The method of producing a migrated seismic cross-section in the form of a plurality of seismic traces comprising the steps of: a. employing machine processing means to generate a directional seismic trace from a plurality of side-by-side amplitude-versus-time locational seismic traces representing seismic waves detected by a series of geophones in a geophone array positioned relative to a datum plane adjacent the surface of the earth; b. repeating step (a) to generate a plurality of directional seismic traces wherein each trace corresponds to a distinct and different moveout corresponding to the difference in arrival time of the seismic waves which created said locational seismic traces; and c. recording at least a portion of each of said plurality of directional seismic traces in a form wherein each of said directional seismic traces appears to emanate from a point on said datum plane and wherein each of said directional seismic traces proceeds away from said point into the subsurface of the earth under investigation in accordance with the detected directional seismic information it represents and in accordance with the distribution of the velocity of the seismic waves within said subsurface under investigation.
 8. The method of claim 1 wherein the amplitudes of selected segments of at least one of said directional seismic traces are modified to emphasize the occurrence of seismic events along said directional seismic trace of seismic waves, said segments being selected whenever predetermined coincidence criteria are satisfied by trace-to-trace comparisons of adjacent directional seismic traces.
 9. A method for the construction of a migrated seismic section, retaining the complex waveforms found on the original seismic recording, comprising: a. machine generating amplitude values for a directional seismic trace by summing a plurality of side-by-side amplitude-versus-time locational seismic traces, said locational traces being relatively time-delayed with respect to each other for a preselected moveout, b. repeating step (a) to generate amplitude values for a plurality of directional seismic traces wherein each trace corresponds to a distinct and different moveout corresponding to the difference in arrival time of the seismic waves which caused said locational seismic traces; and c. for each directional seismic trace, machine gEnerating a curved ray path of a wave front chart having the moveout of said directional seismic trace and a common reference (projection) point representing the mean location on a datum surface related to the earth''s surface of the subsurface formation under investigation, and then d. plotting at least a portion of the complex wave form of said directional seismic trace at a position along said ray path in accordance with the reflection time scale of said wave front chart so that said wave form is positioned in depth and offset to represent the migrated position of a seismic reflector in the subsurface. 